1. Field of the Invention
The present invention pertains to the field of providing power from power source equipment (PSE) to one or more devices which are part of a communications system or communications network, and to managing the power which is supplied to the networked devices.
2. Background Art
Network devices which require power are conventionally referred to in the art as “powered devices”, or “PDs” for short. In this document, for reasons explained further below, such devices will be referred to as “power requiring devices”, or “PRDs”, wherein the terms “power requiring device”, “PRD”, and the plurals thereof are entirely synonymous with the terms “powered device”, “PD”, and the plurals thereof, as conventionally employed in the art.
Conventionally, in a communications system, such as a network environment where cabling is employed to provide power to PRDs, at least two separate cables are connected to each PRD. One PRD cable conveys data to and from the (data communications equipment (DCE), while a second cable supplies each PRD with power from a power supply which is typically separate from the DCE. The disadvantages of this approach have long been obvious. Using two cables increases the physical bulk of cabling which must be wired through the physical environment, demanding more space and making it more difficult to track which cables are serving which functions. If power is supplied to a PRD via a local power outlet, for example, a standard wall outlet, then it may be necessary to locate a separate uninterruptible power supply (UPS) near many or all of the PRDs. As a result, multiple UPS may be required. Some PRDs have required transformers co-located with the PRD, further increasing bulk and complicating deployment efforts. Overall, dual cable solutions typically cost more than a single cable solution and tend to be unwieldy to deploy and maintain.
In addition, a key limitation of dual cable solutions is that they inherently tend to exclude the transmission of data which is related to the power consumption of a PRD. For example, if a PRD is plugged directly into a wall socket, or connected to a wall socket via a dedicated UPS or transformer, there typically does not exist any means to monitor the power delivered to the PRD, nor to regulate the power delivered to the PRD. In turn, this makes it difficult to monitor and control overall network power consumption.
A single cable solution, wherein the single cable carries both data and power, has long been known in certain fields. For example, the cabling employed by the plain old telephone system (POTS) network carries both power and data. Other technologies, such as USB communications systems and IEEE 1392 (“Firewire”) systems, typically are capable of supporting both data and power transmission on a single cable. The advantages of single cable solutions are obvious: Lower cost, half as many wires to be tracked and untangled, and, if all the cables extend from a single DCE, then a single UPS can provide power support to all the network devices via the DCE. Furthermore, single cable solutions are inherently more friendly to technology which monitors and regulates power consumption by the PRDs, since the power cable is already designed to support data transmission as well.
A problem has existed, however, in adapting certain widely used legacy technologies to take advantage of single cable power and data solutions. In particular, Ethernet communications systems, which are widely deployed for wired computer networks worldwide, have long relied on one cable (the Ethernet cable) to carry data to PRDs and another separate cable to supply power to the PRDs, with all the disadvantages already noted above.
Recently a solution has emerged to enable Ethernet networks to take advantage of single cable data and power solutions. Specifically, the IEEE 802.3af protocol defines standards wherein power can be carried to PRDs from a DCE, such as an Ethernet switch, over the same industry-standard Ethernet cabling and Ethernet connectors (i.e., the RJ-45 plug and jack) that formerly was used to carry only data. As a result, where it was formerly necessary to employ a separate source of power to deliver power to PRDs, the power source equipment (PSE) can now be integrated into the DCE itself. Newly designed PRDs, such as wireless access points (WAPs) for 802.11 and Bluetooth devices, web cameras, IP telephones, security access devices, point-of-service (POS) terminals, and similar technologies are designed to accept power directly over the Ethernet cabling, dramatically simplifying deployment of network devices.
The IEEE 802.3af standard is also referred to as the “Power Over Ethernet” standard, or “PoE”, and the terms “802.3af” and “PoE” are used interchangeably in this document, along with such terms as “802.3af-compliant”, “PoE-compliant”, and related terminology.
An advantage of PoE is that a PoE-compliant PSE, or PoE PSE for short, can detect the presence of legacy Ethernet devices which are not designed to accept power over the Ethernet cable, and so not deliver power to such devices. This makes it possible to support both PoE-compliant PRDs and legacy PRDs in the same network. Additionally, legacy Ethernet switches, which are not PoE-compliant, can be used with the newer PoE-compliant PRDs. This is done by inserting, between the legacy Ethernet switch and the PRDs, a so-called “mid-span” PSE, also referred to as a PoE mid-span hub. The PoE mid-span hub accepts the Ethernet cabling from the Ethernet switch, and loads the power onto Ethernet cables which extend from the PoE hub to the PRDs. When data is received from the PRDs, the mid-span PoE hub passes the signals on to the Ethernet switch.
A further advantage of the IEEE 802.3af standard is that PoE-compliant PRDs can have an embedded management information base (MIB), which contains data on the power requirements of the device as determined by the device manufacturer. Specifically, 802.3af-compliant PRDs can be classified at power levels designated as ‘1’, ‘2’, or ‘3’, which respectively indicate increasing power requirements. (A default ‘0’ value encompasses all three power levels. A fifth designation, ‘4’, is currently reserved for future use.) The PoE PSE can read the power classification from a PoE PRD via the Ethernet connection. This enables the PoE PSE to allocate only the designated amount of power to a PRD, which conserves power for other attached devices and contributes to the general goal of efficient power utilization. Yet another advantage of combining data signaling and power delivery over a single cable is that PRDs can be shut down remotely, via control signals sent from the DCE, without the need for a power switch or reset button.
In summary, PoE technology, and similar protocols which may be employed in the context of other kinds of communications links such as USB and Firewire, enable power to be carried over the same cable that is used for data transmission. These technologies further enable intelligent management by DCEs of the power consumption by PRDs.
In spite of the improvements in network power allocation and power management that have come with 802.3af and similar protocols, shortcomings remain. One problem is that, in real-world operation, PRDs often use significantly less power than the maximum power they might request. For example, an 802.3af-compliant PRD might classify itself in Class 2, meaning that the DCE should be able to deliver 7.0 watts to the port to which the PRD is connected, and therefore that at least 7.0 watts should be held in reserve by the DCE to support the Class 2 PRD. However, in actual use, the PRD might never use anywhere near this much power, or possibly the PRD might draw near the maximum power at infrequent intervals, while using dramatically less power most of the time. This might be the case, for example, with a wireless access point that has a light load of wireless devices associated with it.
In addition, it is not always a requirement of the standards that a device provide any power classification. For example, PoE devices are not required to provide a power classification. As a result, when a PoE-compliant PRD is connected to the DCE, and the PRD does not report any power classification, by default the DCE may allocate or reserve the maximum allowed power under the 802.3af protocol, namely 15.4 watts, to the port to which the PRD is connected. This will be the case even if the PRD never actually consumes anywhere near 15.4 watts.
As a result of these factors, the actual power allocated to PRDs, or held in reserve by the DCE to support the PRDs, may be well in excess of the amount of power that these devices actually require to support their operation. If many devices are connected to the DCE, a further result may be that insufficient power is available to power all the devices, leaving some devices effectively non-operational. It is desirable, then, that a means be found to ensure that the minimum possible power is allocated to each PRD, while still ensuring full functionality of each PRD. In turn, this will ensure that the number of PRDs which may actually be allocated power tends to be maximized, while still minimizing overall power consumption.
A further short-coming of existing power technologies is that they provide no way to prioritize attached network devices. That is to say, if insufficient power is available to support the operations of all PRDs attached to the DCE, it may be desirable that some specific PRDs have a higher priority for power allocation than other PRDs. The exact choice of which PRDs should have higher priority will naturally depend on many factors specific to the nature of the network, the usage being made of the network devices, and the specific requirements of a company or other enterprise implementing the network.
Therefore, it is desirable that means be provided so that network engineers can indicate a priority among network devices, such that if insufficient power is available to power all PRDs connected to the DCE, then those PRDs assigned the highest priority are preferentially allocated power ahead of lower priority PRDs whenever possible. It is further desirable that network engineers be provided the maximum possible flexibility in determining the criteria which are used to assign power allocation priority levels to PRDs.
A further shortcoming of present technologies is that, in the event of a sudden decrease in available power, no method is provided to deallocate power from the PRDs. It is desirable that, in the event of an unexpected decrease in available power, a means exist to deallocate power from some of the PRDs, preferably in an order which reflects some kind of priority among the attached PRDs, where that priority may or may not be the same priority used to assign power to the PRDs to begin with.
Given the foregoing, what is needed is a system and method of improved, dynamic power management and allocation for power requiring devices which are part of a communications system or communications network.
In particular, what is needed is a system and method of dynamic power management and allocation for determining the actual power consumption of power requiring devices which are part of the communications system, and adjusting the power allocation so that the minimum necessary power is allocated to power requiring devices which are part of the communications system. What is further needed is a system and method of dynamic power management and allocation for determining a priority among power requiring devices which are part of the communications system, and for ensuring that whenever possible power requiring devices of a higher prior are preferentially allocated power ahead of power requiring devices of a lower priority.